Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guidewire, possibly in combination with other intravascular devices such as stents. A typical balloon catheter has an elongated shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guidewire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are three basic types of intravascular catheters for use in such procedures, including fixed-wire (FW) catheters, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The general construction and use of FW, OTW and SOE catheters are all well known in the art. An example of an OTW catheter may be found in commonly assigned U.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE balloon catheter is disclosed in commonly assigned U.S. Pat. No. 5,156,594 to Keith.
Several characteristics that are important in intravascular catheters include pushability, trackability and crossability. Pushability refers to the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability refers to the ability to navigate tortuous vasculature. Crossability refers to the ability to navigate the balloon catheter across narrow restrictions in the vasculature, such as stenosed vessels or fully and partially deployed stents.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter. The distal portion is the section of the catheter that must track the guidewire through the small tortuous vessels of a patient's vasculature. The size of the distal tip, the flexibility of the distal tip, and lumen diameter all influence the trackability of a catheter. Imparting more flexibility to the distal portion of a catheter, in particular, has been found to improve trackability. Increasing the flexibility within the distal tip improves handling and navigation over a guidewire.
To maximize crossability, the present invention is a catheter having a distal tip incorporating high column stiffness. Longitudinal column stiffness permits the distal portion of a catheter to cross narrow lesions within the vasculature. Flexible distal tips can yield to the pressures required to cross such lesions, thereby rendering the catheter ineffective. Further crossability is improved by the physician withdrawing the thinner, more flexible guidewire, and replacing it with a thicker and stiffer guidewire. Thicker guidewires add desirable stiffness when crossing tight or totally occluded lesions within the vasculature. Passage across such lesions often requires a greater longitudinal stiffness than a thinner guidewires affords. Advancing a thicker guidewire over the distal tip achieves this required longitudinal stiffness. Many catheter designs, however, cannot accommodate the replacement of a thicker guidewire. Often, the thicker guidewire is prevented from advancing through a catheter's distal-most tip that is designed specifically for thinner guidewires. The smaller distal tip openings of these catheters allow for easier navigation when used in combination solely with thinner gauge guidewires.